<template>
	<ul class="list">
		<li class="item" v-for="item of letters" :key="item" :ref="item" @click="handleLetterClick" @touchstart.prevent="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd">{{item}}</li>
	</ul>
</template>

<script>
export default {
	name: 'CityAlphabet',
	props: {
		cities: Object
	},
	computed: {
		letters () {
			const letters =[]
			for(let i in this.cities) {
				letters.push(i)
			}
			return letters
		}
	},
	data () {
		return {
			touchStatus: false,
			startY: 0,
			timer: null
		}
	},
	updataed () {
		this.startY = this.$refs['A'][0].offsetTop
	},
	methods: {
		handleLetterClick (e) {
			this.$emit('change',e.target.innerText)
		},
		handleTouchStart () {
			this.touchStatus = true
		},
		handleTouchMove (e) {
			if(this.touchStatus) {
				if (this.timer) {
					clearTimeout(this.timer)
				}
				this.timer = setTimeout(() => {
					const touchY = e.touches[0].clientY - 79
					const index = Math.floor((touchY-this.startY) / 20)
					if (index >= 0 && index < this.letters.length) {
						this.$emit('change',this.letters[index])
					}
				},16)
			}
		},
		handleTouchEnd () {
			this.touchStatus = false
		}
	}
}	
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl'
.list
	//垂直方向上居中
	display: flex
	flex-direction: column
	justify-content: center
	
	position: absolute
	top: 1.58rem
	right: 0
	bottom: 0
	width: .4rem
	.item
		line-height: .4rem
		text-align: center
		color: $bgColor
</style>